# Depending on your version, you may need:
no warnings 'experimental::smartmatch';

# I have two arrays, @rows and @data
# @data is a pre-loaded array of strings (~60k elements)
# @rows is a much larger array of strings (~600k elements)

foreach my $rawData (@rows)
    {
        if( $rawData ~~ @data )
        {
                # don't do anything, already in array
         } else {
                push(@data,$rawData)
         }
    }